1. Field of the Invention
The present invention relates to a fuel injection control device for a direct injection type internal combustion engine adapted to directly inject fuel into a combustion chamber in an internal combustion engine. More particularly, the present invention is concerned with a fuel injection control device constructed such that a fuel spray is supplied in conformity with an operating condition of the internal combustion engine.
2. Description of Related Art
Relating to direct injection type internal combustion engines, heretofore, fuel injection control devices adapted to supply fuel in a spray form appropriate for an operating condition of the engines are disclosed for example in Japanese patent unexamined publication No. 2000-97030 (pages 4-6 and FIG. 3), Japanese patent unexamined publication No. Hei 10-318096 (page 9 and FIG. 7), and Japanese patent unexamined publication No. 2002-161790 (pages 2-5 and FIGS. 1-6).
The above '030 document discloses a cylinder injection (direct injection) type internal combustion engine and a fuel injection valve for cylinder injection are disclosed. In this document, it is also described that the internal combustion engine constructed to switch an operating mode between a premix combustion mode and a stratified charge combustion mode is adapted to change fuel spray characteristics according to the selected operating mode. More specifically, it is arranged that a fuel spray from the fuel injection valve takes a spray pattern having a substantially axis-symmetric shape with respect to a nozzle hole axis for a first predetermined distance from the nozzle hole and another spray pattern having a substantially point-symmetric or line-symmetric shape in which a sectional shape perpendicularly intersecting the nozzle hole axis spreads in one direction perpendicularly intersecting the nozzle hole axis, for a second predetermined distance or more longer than the first predetermined distance. In the operating mode of the stratified charge combustion, a fuel spray is formed in about the first predetermined distance during a compression stroke of a piston. In the operating mode of the premix combustion, a fuel spray is formed in about the second predetermined distance or more during a suction stroke of the piston.
The '096 document discloses a fuel injection valve capable of injecting a so-called composite spray (a solid spray) including a fuel spray for good combustibility and a fuel spray for good ignitability, and also an internal combustion engine using the fuel injection valve. More specifically, it describes a fuel injection valve provided with a nozzle body having an injection hole, a valve body, and drive means for driving the valve body in its axial direction in order to produce, as the solid spray, a spray with a short fuel spray travel and an increased spray angle by decreasing an inertia force and a spray with a decreased spray angle by increasing the inertia force. This fuel injection valve is constructed such that two turning force giving means for giving a turning force to fuel are axially arranged upstream from the injection hole and a first turning force giving means and a second turning force giving means of the two turning force giving means are different in structure.
The '790 document discloses a combustion control device for a direct injection/spark ignition type internal combustion engine. This device is provided with a fuel injection valve for directly injecting fuel into a combustion chamber and a spark plug. The device is constructed to selectively conduct a stratified charge operation in which a spray is concentrated near the spark plug and a uniform operation in which a spray is uniformly dispersed throughout the combustion chamber. This document also describes separate injection control means which executes fuel injections several times per one cycle during the uniform operation. This separate injection control means makes a time interval between injections and a rate of injection quantity variable according to a rotational speed of the internal combustion engine and a load on the engine.
In general, a fuel spray pattern (a fuel spray which an air-fuel mixture is collected up near the spark plug) required for the stratified charge combustion and a fuel spray pattern (a high dispersion fuel spray which an air-fuel mixture is dispersed throughout the combustion chamber) required for the uniform combustion have opposite characteristics. The devices disclosed in the above documents '030 and '096, however, could realize only one fuel spray pattern similar to the fuel spray pattern for the stratified charge combustion. Specifically, it is impossible to effectively achieve the uniform combustion and to select one from two or more combustion patterns, so that engine performances could not be improved.
In the device disclosed in the document '790, fuel injections are performed in several times, leading to plural transient response times of the injection valve, during which fuel atomization would deteriorate. This results in an increase in diameter of a fuel spray particle, which decreases resistance of the air to the fuel spray and thus increases a fuel spray travel (distance). Further, the fuel spray travel has a large influence mainly on an injection quantity (an injection rate) per unit of time. Accordingly, this device could not easily shorten the fuel spray travel as mentioned above even if the fuel injections are performed in numbers. In the uniform combustion, when an engine rotational speed is low at for example idle engine operation, the time intervals for plural injections can be provided. However, when the engine rotational speed is high at full-load engine operation, there is not sufficient time for plural injections. The device in the document '790 have to inject a large quantity of fuel and therefore could not provide a fuel spray adequate for the above mentioned uniform combustion by the plural injections.